It is generally known to utilize plastic packaging to reduce exposure of products to atmospheric conditions, such as to moisture or oxygen, which may damage the products. For example, packaging for foodstuffs is well known, in that moisture and oxygen may cause the foodstuffs to become spoiled and inedible or otherwise undesirable. In addition, many products in the medical field, for example pharmaceutical products, nutraceutical products, and devices such as absorbable sutures, drug coated medical stents or other medical devices, may also be very sensitive to atmospheric moisture.
Typically, moisture-sensitive products may be encased in thermoplastic material that is relatively impermeable to water molecules. Specifically, many polymeric materials are utilized as barriers to moisture transmission. For example, a film of high density polyethylene (HDPE), or polyvinylidene chloride-methyl acrylate (PVdC-MA) copolymer may be utilized to restrict the movement of water molecules through the film. Oriented polypropylene, metallized oriented polypropylene, or metallized polyester would also be useful as moisture barrier material. In addition, metal foil is known to prevent the transmission of oxygen and/or moisture through polymeric packaging having a layer of metal foil contained therein.
Although these moisture barrier polymers may be useful in restricting the movement of moisture into a package, some moisture molecules can still make their way into the package to deleteriously affect the product contained therein. In addition, even when barrier materials are effective at restricting the transmission of water molecules through a package, certain features of the package may still allow for the transmission of water molecules. For example, where a barrier material is incorporated into a central layer of a film structure and the film structure is sealed to another film structure having a barrier material as a central layer, the edges of the package may not be protected by the barrier layers. This may allow moisture to make its way into a package along the edges of a heat sealed package.
One solution to maintaining a particularly low or virtually nonexistent level of moisture within a package is to incorporate sachets of desiccant material into the internal space of the package to remove the moisture from the headspace of the package. A sachet may effectively maintain a very low level of moisture in internal spaces of packages, but may have difficulty maintaining the same consistent moisture levels after the package has been opened and a product has been removed. For example, a typical package of moisture-sensitive products may contain a plurality of the products. A sachet of desiccant material incorporated into the package may only guarantee that moisture level of the package is maintained at a constant or minimal moisture level until the package is opened and the first product is thereby removed. The remaining products will be instantly exposed to atmospheric moisture when the seal of the package is broken. Although the sachet may remove some moisture from the headspace of the package after the package is opened, the remaining moisture-sensitive products, having already been exposed to moisture, may already be damaged. This may be especially true in bulk packaged materials where sachets are most often used. Desiccant materials are typically incorporated into liddings of jars or in sachets of multi-unit packages.
In addition, sachets of desiccant material may become saturated with atmospheric moisture relatively quickly thereby decreasing or eliminating their effectiveness. Moisture-sensitive products, therefore, stand a greater chance of being damaged by moisture in this case.
Moreover, the desiccant material contained in the sachets is typically in powder or granular form and may leak or otherwise spill from the sachets thereby contaminating the product or products contained within the package. For example, if the desiccant material contacts a food, pharmaceutical or nutraceutical product or medical device, the food, pharmaceutical or nutraceutical product or medical device may become contaminated with the desiccant material, which may be damaging to the health of an individual that consumes the food product or uses the medical device. In addition, spilled or broken desiccant sachet contents could create a deleterious effect on the efficacy of the medical device, such as a drug eluting stent (DES).
Additionally, although desiccant material is generally known to reduce the moisture content within a package, typical desiccant materials are “physical” desiccant materials, such as molecular sieves, that bind water molecules within pore spaces of a material. Typically, physical desiccant materials absorb water at all humidity levels, but will cease to absorb water when interstices of the physical desiccant material are filled. Therefore, physical desiccant materials may be ineffective at high humidity levels.
An additional type of desiccant material may be hydrate forming agents such as salts. Typical salts that may be utilized as desiccant material are sodium phosphate di-basic, potassium carbonate, magnesium chloride, calcium chloride, and calcium sulfate, although many others are known as well. Typically, the drying capacity is greatly influenced by the relative humidity within a package. Generally, no water is taken up by the hydrate-forming agent until the relative humidity reaches a value at which the first hydrate forms. In the case of calcium chloride, for example, the first hydrate occurs at less than about two percent relative humidity (RH). Water is then taken up by the hydrate forming salt until the first hydrate is completely formed by the salt. No further water is taken up by the salt until the relative humidity reaches a second level where the second hydrate forms. This process continues through as many hydrates as the agent forms at which point the substance begins to dissolve and a saturated solution is formed. The saturated solution will then continue to take up water.
Although these salts may be effective at removing water molecules from a quantity of gas that may be contained within the headspace of a package, since the salt only binds the water molecules within the salt, the water molecules may easily escape back into the package. This is known as breathing, and may cause deliquescence (water droplets and liquidization) inside the package. Typically, this can happen if the salt becomes saturated and if the temperature of the package increases, or if the pressure of the package decreases, which may occur during shipment or storage of the package.
In addition, salts may not allow moisture levels within a package to fall to a level that is necessary to protect the moisture-sensitive product that may be contained within the package. Typically, since salts have different levels of hydration, humidity levels may remain at certain level without decreasing until the level of hydration changes.
However, these salts may be utilized to maintain certain humidity levels within the headspace of a package. For example, certain products may require that a certain level of moisture or humidity be maintained within the package headspace. Headspace humidity control for products can be manipulated by incorporation of the appropriate hydrate forming agents.
The present invention may utilize chemical desiccant technology, which is more preferable because the moisture level within a package may be maintained at an extremely low level. Chemical desiccant materials chemically react with water molecules to form a new product, wherein the water molecules are chemically incorporated into the new product. For example, calcium oxide binds water in the following reaction:CaO+H2O→Ca(OH)2 
Because the reaction noted above requires very high energy levels to reverse, it is, for all practical purposes, irreversible. Chemical desiccant materials typically absorb water at all humidity levels, and will continue to take up water at high relative humidity levels. These chemical desiccant materials, therefore, may reduce levels of moisture within the package headspace to zero or near zero, which is often desired to maintain maximum dryness of the product.
Examples of typical packages or products that would benefit from desiccant material are medical kits, such as home pregnancy test kits and medical instruments. In addition, other products include electrostatic shielding packaging for electronic parts, such as printer cartridges, circuit boards, televisions, DVDs, printers, modems, personal computers, and telecommunications equipment, etc. Further, other packaging that would benefit from desiccant material is packaging for foods, such as cheese, peanuts, coffee, tea, crackers, spices, flour, bread, etc. In addition, other products that would benefit from desiccant material incorporated into the packaging are shoes, boots, film products and cameras, and products that may be shipped by sea, such as high-value wood like mahogany that would be damaged if exposed to ambient humidity typically found in cargo ships.
A need, therefore, exists for polymeric plastic packaging that may be used in packaging to preserve products that may be sensitive to atmospheric moisture. The packaging may comprise films having a desiccant material incorporated directly into the film. In addition, films are needed that effectively control the level of moisture within packaging without using sachets or desiccant beads that may become ineffective over time, or that may contaminate products contained within the packaging. Moreover, films, methods of use and manufacture are needed to overcome the additional disadvantages as noted above with respect to sachets, beads or physical desiccants.